1. Field of the Invention
The present invention generally relates to image forming devices, and particularly, to an image forming device such as a dual-sided printer and a duplicator which is capable of both-side printing as well as one-side printing.
2. Description of the Related Art
FIG. 1 is a schematic diagram showing a conventional dual-sided printer 10 which is capable of both-side printing. The dual-sided printer 10 is comprised of a photoreceptor drum 11, a face-down stacker 12 which is located above the photoreceptor drum 11, a recording medium switchback portion 13 which is located in a side direction of the photoreceptor drum 11, a recording medium ejection path 14, a manual paper inlet through which a recording medium 92 (93) is introduced, and a paper cartridge 17. The face-down stacker 12 is capable of storing printed papers with a latest printed surface facing downward, i.e., the stacker 12 is capable of storing the printed papers in order of page numbers without requiring large memory. The recording medium switchback portion 13 functions as a transfer means for receiving a paper, one surface (upper surface) of which is printed by passing the photoreceptor drum 11, and transfers the paper in the reversed direction in order to perform a printing of the other side of the paper.
In the dual-sided printer 10, the both-side printing is carried out as follows. When a paper is fed from the paper cartridge 17 in the direction A shown in FIG. 1, it is passed underneath the photoreceptor drum 11 as indicated by the arrow B and its upper surface is printed. Then, the paper is transferred in the direction C and reaches the recording medium switchback portion 13. At the recording medium switchback portion 13, the direction of the paper transfer is reversed and it is fed in the direction indicated by the arrows D and E towards a position underneath the paper cartridge 17 (the movement of a paper from the paper cartridge 17 to the position underneath the paper cartridge 17 is hereinafter referred to as a first run of the paper). The position of the paper which may be shifted during the first run may be adjusted by a paper position adjusting mechanism (not shown). After this, the paper is transferred in the direction indicated by the arrow F and passed again underneath the photoreceptor drum 11 so that the other side of the paper is printed. The paper, both sides of which are printed, is then moved in the direction indicated by the arrow G and is stored on the face-down stacker 12 (the movement of a paper from the position underneath the paper cartridge 17 to the face-down stacker 12 is hereinafter referred to as a second run of the paper).
In a case that only one side of the paper is necessary to be printed, a paper is transferred in a sequence as indicated by the arrows A.fwdarw.B.fwdarw.G and ejected to the face-down stacker.
Since the face-down stacker 12 is located above the photoreceptor drum 11, the recording medium ejection path 14 is curved in an arc shape and the paper passed underneath the photoreceptor drum 11 is transferred through the ejection path 14 in a curved state to the face-down stacker 12.
Now, there are cases that a recording medium having a relatively high strength or rigidity, such as a postcard, an OHP sheet or an envelope, is put through the manual paper inlet to the dual-sided printer 10 so that one side of the recording medium is printed with names, addresses, articles and so on. This kind of use of a dual-sided printer is occasionally required and is nothing uncommon.
However, in the conventional dual-sided printer 10, the recording medium having a relatively high strength does not curve easily in accordance with the shape of the ejection path 14 after one side of which is printed by passing underneath the photoreceptor drum 11. Thus, the transfer of the recording medium to the face-down stacker 12 may not be carried out smoothly and sometimes a jamming of recording media occurs. That is, it is not easy to perform one-side printing for a recording medium having a high rigidity using the conventional dual-sided printer 10.